The art of innovation

Laura Hopperton talks to the GE Intelligent Platforms team about its award winning design.

Earlier this month, GE Intelligent Platforms won the award for best overall design at Mentor Graphics' annual Technology Leadership Awards (TLA). The team, based in Towcester, created the SBC612, a 6U VPX single board computer that has more than 3500 nets, 11,000 vias, 20,000 connections and 8500 components – including 20 BGAs placed on both sides of the board. The 18 layer pcb stackup also uses several quad flat packs with a pitch of just 0.4mm.

Now entering its 23rd year, Mentor Graphics' competition seeks to recognise engineers and cad designers who use the company's technology to address complex pcb systems design challenges and produce industry leading products. The SBC612, designed using Expedition Enterprise, has been developed to deliver a step forward in performance for military applications such as intelligence, surveillance and reconnaissance, electronic warfare and mission computing.

The team, led by hardware designer Paul Curran, entered the competition last year with a commercial off the shelf (COTS) multiprocessor board aimed at rugged defence and aerospace applications such as radar, sonar, signal intelligence and image processing. While the engineers said they were happy to have won the Military/Aerospace award, they wanted to go 'one further' this time around. "We completely changed the layout and processor from our design last year as it needed to be faster, lighter, lower powered and add in new features," said pcb designer Rob Savage.

"The design jumped from the dual core version to an octocore processor," added Curran. "The complexity was in taking a fast processor, dual channel DDR3 memory, medium speed SATA, multigigabit fabrics with PCI-Express, and RapidIO, and blending all of them into a space constrained form factor."

At the heart of the innovative technology is the latest Freescale QorIQ P4080 processor, with eight e500mc cores operating at up to 1.5MHz. These eight cores were designed to offer 'exceptional flexibility' to system designers, with both symmetric and asymmetric multiprocessing architectures being supported. It is also possible to host multiple operating systems on the same device.

Mentor's software enabled the team to execute its highly complex design in a much quicker time, according to Curran. "The Mentor Graphics toolset made it possible for us to take a highly flexible approach to constraint management and allowed us to integrate the design of the FPGAs on the board interactively with the pcb design process itself," he said. This meant the team could optimise pinout within constraints and specify pins for clocks as well as other functions.

One of the major challenges the team faced was handling the shift from parallel buses to serial fabrics. The team also had to meet the technology constraints on space and denser packed components, whilst being sensitive to cost.

For pcb designer Mike Tapp, the main design issue was routing. "The board is very dense, so routing was complex. But this is the kind of thing we're good at," he said. "The project took five months from start to finish, but mil/aero needs to be designed for ruggedness – you can't just throw it down to autoroute."

According to Tapp, the team only ran the router overnight to highlight the 'difficult bits'. "If the routing 'fell over' without any constraints on, then we knew it was going to be difficult to route manually when we applied constraints," he noted. "What it hadn't done by morning flagged up the tough parts we needed to add layers to or tweak in some way."

The difficulty in routing was also exacerbated by the power devices, which had to be placed closest to the processor and directly between the processor and the DDR3/FPGAs. Despite this, Tapp said he was extremely pleased with the outcome. "The rev 1 board just worked," he said. "Populate, plug in and bingo! We were all very pleased."

One of the many innovative features on the board is the Trust Architecture. This is a series of processor technologies designed to provide users with additional security functionality to prevent loss of control of system functionality, loss of data to an unauthorised party and loss of IP through reverse engineering.

In addition, for many legacy applications based on the Power Architecture, it allows a multi slot configuration to be reduced to a single slot, saving size and weight. "To fit the board in a single slot imposed a number of height constraints, with a knock on impact for the thermal design," asserted Curran. "We had to accommodate 14 power rails on just two internal plane layers and, to shield the remaining signals from the voltage rails, a ground layer had to be placed on either side, creating a four layer middle section."

As its power envelope is equivalent to that of previous dual core processors, the board can also permit the addition of new functionality without exceeding the application's current power envelope. For new applications, the SBC612 has been designed to enable the development of compact, low weight solutions with 'significantly more performance' than has previously been possible.

"Significant effort was taken to ensure thermal efficiency, effective power delivery and sufficient routing channels, including tuning space," said Rick Hartley, senior engineer and TLA judge. "The pre-layout planning, coupled with concurrent design process, even resulted in the team finishing the design approximately two weeks earlier than scheduled."

The judges said they were impressed that GE's design had through hole boards with interconnect densities of 372pins per square inch. One judge even commented that it was the best he had seen. "Through hole normally gets between 6 and 12% efficiency, but this was an exceptional layout with 27%," he said.

"It's good to see the designs we're working on judged to be leading edge by independent observers," noted Curran. "It's not often you get to compare your work against others and it's good to have our day to day labours recognised."

Savage also commented that, while many awards are given out to a vendor's favourite customer, this one meant more because it was judged by industry peers, "Real people who understand the job," he concluded.

The full team included Paul Curran, Michael Tapp, Rob Savage, and John Digby.